The present invention relates to a fastening tool for applying plastic parts to objects wherein the plastic parts are supplied in the form of a belt in which the plastic parts are linked together by means of at least one flexible web, wherein the fastening tool is designed to transport the belt by means of a feed mechanism such that one plastic part at a time is delivered to a fastening position, and wherein the feed mechanism has a fluid drive that is coupled by a translation-rotation converter to a transport gear that is rotatably mounted on the fastening tool and is designed to positively or nonpositively engage the belt in order to transport it.
Such a fastening tool is known from DE 196 43 656 A1.
In many areas of prior art, it is necessary to attach parts to objects, for example nails in wooden objects, screws in wooden objects, plastic parts on metal objects such as metal sheets, etc.
The attachment of plastic parts, frequently called clips, to prepared or unprepared metal sheets, for example to welding studs, is an economically important field. In the automotive field, a variety of such plastic parts are attached to the vehicle body to perform holding functions, for example to support instrument panels, hold interior trim, carpeting, brake lines, electrical wiring, etc.
Since it is frequently necessary to attach a number of identical plastic parts in various positions in rapid sequence, the appropriate feeding of the plastic parts and the proper positioning of the plastic parts in the correct orientation prior to the actual fastening process is especially important.
It is an industry standard to provide the plastic parts as bulk material and then to separate them (using a vibrator, for example). Subsequently, one plastic part at a time is brought into fastening position by means of an appropriate feeding device.
Alternatively, there is known from EP 0,506,307 B1 a belt wherein the plastic parts are linked one after the other. Here, the plastic parts are molded onto one or two flexible webs during their molding process (generally by injection molding), where the flexible webs are either joined to other flexible webs or are fed into the injection molding machine as a continuous web. The belt is rolled up and transported to the production site in the rolled-up state.
This method of supplying plastic parts is offered by the company Tucker GmbH under the name “Plastifast.”
A fastening tool for attaching plastic parts supplied in this form is known from the aforementioned DE 196 43 656 A1.
In this prior art, the fastening tool has a housing with a handgrip. Supported on the housing is a magazine with two longitudinal webs into which the belt with the plastic parts is inserted. From there, the plastic parts are delivered to a head wherein the plastic parts are deflected in curved guides. Also located on the head is a feed mechanism to transport the belt.
The feed mechanism has a transport gear that positively engages the belt. The transport gear is coupled to a pneumatic drive by a translation-rotation converter. The translation-rotation converter has a number of laterally projecting pins at the transport gear. The pitch of these pins corresponds to the pitch of the teeth on the outer circumference of the transport gear.
The pneumatic drive has a carrier element that moves translationally back and forth and that “catches” one pin during each backward motion and “pushes against” one pin in front of it during each forward motion in order to turn the transport gear.
A complicated ratchet mechanism makes it possible for the carrier element to move backwards without moving the transport gear backwards.
The feed mechanism disclosed in this document can be improved from both functional and design standpoints. In order to ensure that a plastic part arrives at a fastening position every time even when problems arise in the transport mechanism, an external handwheel is provided by means of which the transport gear can be turned by hand.
Known from EP 0,131,851 A1 is a device for inserting and/or removing screws. In this device, screws are automatically fed, wherein the screws are inserted into a strip-shaped magazine and are pushed into a fastening position by spring pressure.
A similar mechanism is also known from U.S. Pat. No. 2,943,652.
A “machine-gun-style” lateral feeding of strips of nails to a fastening tool is known from DE 3,606,901 A1.
In addition, a fastening tool for inserting screws is known from U.S. Pat. No. 5,144,870. The screws are fed from a belt into a guide. The screws are fed by a spring-loaded drive oriented in the longitudinal direction which has a gear rack which an elastically-preloaded tooth engages.
All of the above-mentioned solutions for fastening tools are either very costly or not very reliable in their designs.